title: Diels-Alder reaction for tumor pretargeting: in vivo chemistry can boost tumor radiation dose compared with directly labeled antibody.
abstract: Current pretargeting systems use noncovalent biologic interactions, which are prone to immunogenicity. We previously developed a novel approach based on the bioorthogonal reaction between a radiolabeled tetrazine and an antibody-conjugated trans-cyclooctene (TCO). However, the tumor-to-blood ratio was low due to reaction with freely circulating antibody-TCO.
  
  
  METHODS
  Here we developed 2 tetrazine-functionalized clearing agents that enable rapid reaction with and removal of a TCO-tagged antibody (CC49) from blood. Next, we incorporated this approach into an optimized pretargeting protocol in LS174T-bearing mice. Then we compared the pretargeted (177)Lu-labeled tetrazine with (177)Lu-labeled CC49. The biodistribution data were used for mouse and human dosimetry calculations.
  
  
  RESULTS
  The use of a clearing agent led to a doubling of the tetrazine tumor uptake and a 125-fold improvement of the tumor-to-blood ratio at 3 h after tetrazine injection. Mouse dosimetry suggested that this should allow for an 8-fold higher tumor dose than is possible with nonpretargeted radioimmunotherapy. Also, humans treated with CC49-TCO-pretargeted (177)Lu-tetrazine would receive a dose to nontarget tissues 1 to 2 orders of magnitude lower than with directly labeled CC49.
  
  
  CONCLUSIONS
  The in vivo performance of chemical pretargeting falls within the range of results obtained for the clinically validated pretargeting approaches in mice, with the advantage of potentially allowing for fractionated radiotherapy as a result of a lower likelihood of immunogenicity. These findings demonstrate that biologic pretargeting concepts can be translated to rapid bioorthogonal chemical approaches with retained potential.
authors.affiliation: Department of Minimally Invasive Healthcare, Philips Research, Eindhoven, The Netherlands; and.
authors.forename: Raffaella
authors.initials: R
authors.lastname: Rossin
authors.forename: Tilman
authors.initials: T
authors.lastname: Läppchen
authors.forename: Sandra M
authors.initials: SM
authors.lastname: van den Bosch
authors.forename: Richard
authors.initials: R
authors.lastname: Laforest
authors.forename: Marc S
authors.initials: MS
authors.lastname: Robillard
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000627:therapeutic use*; D061565:Cycloaddition Reaction; D034242:Cyclooctanes / Q000737:chemistry; D005260:Female; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry; D006801:Humans; D007553:Isotope Labeling / Q000379:methods*; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D058990:Molecular Targeted Therapy; D009369:Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011829:Radiation Dosage; D011874:Radiometry; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed
chemical_list: D000911:Antibodies, Monoclonal; D034242:Cyclooctanes; D006573:Heterocyclic Compounds, 1-Ring; C474479:cyclooctane
keywords: 177Lu; Diels-Alder; clearing agent; dosimetry; pretargeting